rod bearing clearance
rod bearing clearance
(OP)
I am working on a smallblock chevy and getting rod bearing clearances of .0045. I am looking for a clearance of .0025. I have a new crank that is measuring 2.099, in spec. but on small side, and new rods that are measuring 2.2252, in spec. but on the big side. I am using a micrometer and dial bore gauge to get these specs. I have tried 2 differant bearing brands,that came out to .0045. I have also tried a bearing that will give you .001 less and it came out to .0035. I am racing and need a chamferd bearing and can't find one that will give me .002 less clearance. I can't return the crank or the rods since both manufacturers say they are in spec. My question is if i have the rods reconditioned on the small side 2.2247 what will that do for my clearances. I dont think the answer is .0005 less because i think the bearing will exagerate the half thousandts.





RE: rod bearing clearance
RE: rod bearing clearance
RE: rod bearing clearance
RE: rod bearing clearance
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: rod bearing clearance
I built an engine once that had new rods and a turned crank, when the rod bearing clearance was checked it was .003 a little more than i like but i ran it. When it came time for a rebuild i asked for the rods to be reconditioned to the small side of spec. and then the clearances came out to .002, but i never checked the id. of the rods before or after,when i built that engine, just the bearing clearance. I know it makes a differance,but i would like to know how much smaller .0005 in the id. of the rod will do to my bearing clearance. Would like to hear from some shops that have done this and know what differance it will make. Thanks everyone.
RE: rod bearing clearance
I have always found that with crank spot on middle of spec, and rods on min spec (maximum crush, and 0.001" OD bearings, I have always ended up with between 0.002 and 0.003" clearance in the axis of the rod direction.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: rod bearing clearance
I have not personally done this but I expect a decent approximate answer to your question can be estimated by comparing the relative structural stiffness (thickness) of the rod compared to the bearing shell. If the rod is four times thicker than the bearing shell then I would expect a .0005 inch rod bore change to effect a .0004 journal clearance change.
If you need to know closer than this you'll either have to test it or perhaps a bearing manufacturer could answer the question.
RE: rod bearing clearance
Check the bore that the bearings fit in if they are on spec. I'd take the bearings back. Try another manufacture.
RE: rod bearing clearance